Great, great day with Trailhead. I opted for Thriller and was not disappointed. There's a fair amount of climbing on doubletrack, so I wouldn't recommend this ride to someone who doesn't have a great deal of fitness. However, the incredible views of Chiang Mai on the way to the top of the mountain are worth the price of the tour alone.
Lek (my guide) and Mong (who overseas the tours) were great- funny, friendly, etc. I didn't feel like a customer at all; more like heading out on a ride with two new friends. Lek is an excellent rider and great guide. I was fortunate to be the only rider the day of my tour, so Lek was kind enough to extend our ride by tacking on some extra trails.
In addition to providing me with an excellent lunch during the ride (and catering to my vegetarian diet), we grabbed lunch at the end of the day.
I can't recommend these guys enough. There are a slew of outfits in Chiang Mai offering mountain bike trips, but none that can match the service and quality of what Trailhead has.
I'll be back.